Communication systems utilize power amplifiers to boost signals for prior to transmitting, such as transmitting via an antenna. Two important characteristics for amplifiers used in such systems are gain and power efficiency.
The gain of an amplifier is the measure of the ability of an amplifier to increase an output signal from an input signal. It is important that the gain be at the right value. Additionally, it is important that the gain be relatively constant for varied input values and frequencies. Variations in gain can lead to distorted signals upon transmission. Thus, a relatively constant gain, without variations according to input signal values, is needed.
The power efficiency is the ratio of output power to input power. Some amplifiers may only be efficient when the input signal has a high value. In others, the efficiency may depend on frequency.
A challenge faced by amplifier designers is to provide constant gain while also having high power efficiency. Often, improving gain comes at the expense of power efficiency and improving power efficiency comes at the expense of not having a constant gain.